The invention relates to a pedicle screw and an assembly aid therefor.
For the replacement of vertebra of the human spinal column, for the distraction of the spinal column, for the stabilization of the vertebrae and likewise, it is known to apply so-called pedicle screws. They are screwed into the pedicle of the vertebra and comprise a head which is connected to suitable provisions, for example to a stabilizing system, to distraction rods and likewise. It is known to provide pedicle screws with a ring-like head which on the end faces comprises a toothing. It is however also known to form the screw head fork-like so that with this it is in the position to accommodate a distraction rod, a connecting rod or likewise. For fastening the rod in the fork-like head a suitable screw element may be brought into engagement with the head. The screw element may be hat-like and be screwed onto outer threaded sections of the head. It is however also known to allocate an inner thread to the head sections for receiving a set screw or likewise with which the applied rod may be fastened in the head.
It is further known for a more simple handling of the pedicle screw to provide this with a head which is movable relative to the shank, preferably pivotable in all directions. For this purpose the head end of the shank may be formed ball-like, wherein the ball surface cooperates with a spherical bearing surface in the head. In this case it is necessary, after the adjustment of the shank and head to one another has been effected, to retain this angular position. This may for example be effected in that the rod accommodated by the head is pressed against the ball-like head of the shank, by which means the parts are fixed in their position to one another.
In the treatment generally first the pedicle screws are rotated in. Subsequently the insertion of the rod is effected. With this however under certain circumstances considerable forces must be applied in order to move the rod into the fork-like head. The introduction force must be maintained for so long until with the help of the screw element a sliding out of the receiver in the head is no longer possible. For this a considerable amount of dexterity and also a considerable force effort must be carried out on the part or the surgeon.